Piston Design for Downhole Pulser

ABSTRACT

A measurement while drilling (MWD) tool includes a sensor, an encoder operably connected to the sensor and a pulser operably connected to the encoder. The pulser includes a linearly acting bidirectional piston that operates a poppet valve. The poppet valve is designed to completely or partially interrupt the flow of fluid through the MWD tool. The selective operation of the piston-driven poppet valve creates pressure signals that are carried through the fluid. The piston assembly that drives the poppet valves includes wear rings that improve the performance and durability of the piston.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/159,131, filed May 8, 2015, entitled “Improved Piston Design for Downhole Pulse,” the disclosure of which is incorporated herein.

FIELD OF THE INVENTION

This invention relates generally to the field of telemetry systems, and more particularly, but not by way of limitation, to acoustic signal generators used in wellbore drilling operations.

BACKGROUND

Wells are often drilled for the production of petroleum fluids from subterranean reservoirs. In many cases, a drill bit is connected to a drill string and rotated by a surface-based drilling rig. Drilling mud is circulated through the drill string to cool the bit as it cuts through the subterranean rock formations and to carry cuttings out of the wellbore.

As drilling technologies have improved, “measurement while drilling” techniques have been enabled that allow the driller to accurately identify the location of the drill string and bit and the conditions in the wellbore. MWD equipment often includes one or more sensors that detect an environmental condition or position and relay that information back to the driller at the surface. This information can be relayed to the surface using acoustic signals that carry encoded data about the measured condition.

Prior art systems for emitting these acoustic signals make use of wave generators that create rapid changes in the pressure of the drilling mud. The rapid changes in pressure create pulses that are carried through the drilling mud to receivers located at or near the surface. Prior art pressure pulse generators include the use of rotary “mud sirens” and linearly-acting valves that interrupt the flow of mud through the pulse generator. The temporary flow disruption can be used to create a pattern of pressure pulses that can be interpreted and decoded at the surface.

Although generally effective, prior art piston-based pulsers suffer from several deficiencies. In particular, the prior art pistons have a tight tolerance within the pulser tool. The tight tolerance accelerates wear and can lead to premature failure of the pulser. In certain situations, the tight tolerance between the piston and the receiving bore can cause the piston to become pressure-locked within the bore. Once locked, the pulser will no longer function. Accordingly, there remains a need for an improved piston pulser design that overcomes these deficiencies in the prior art.

SUMMARY

In various embodiments, the present invention includes an acoustic pulse generating component for use in connection with a downhole drilling tool. The acoustic pulse generating module includes a piston assembly and a drive assembly configured to move the piston assembly. The piston assembly includes a piston having a low friction wear ring.

In another aspect, the present invention includes a drilling tool that has a sensor, an encoder operably connected to the sensor and a pulser operably connected to the encoder. The pulser includes a piston assembly and a drive assembly configured to move the piston assembly. The piston assembly includes a piston having a low friction wear ring.

In yet another aspect the present invention includes a measurement while drilling (MWD) tool that includes at least one sensor configured to output a measurement signal representative of a measurement of a condition selected from the group consisting of torque, inclination, magnetic direction and position. The MWD tool further includes an encoder configured to encode the measurement signal into a command signal and a pulser operably connected to the encoder and configured to transmit an acoustic signal through a fluid medium in response to the command signal. The pulser includes a piston assembly and a drive assembly configured to move the piston assembly. The piston assembly includes a piston having a wear ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a drilling system constructed in accordance with an embodiment of the invention.

FIG. 2 is a cross-sectional view of an embodiment of the pulser module of the drilling system of FIG. 1.

FIG. 3 is a perspective view of the piston of the pulser module of FIG. 2.

WRITTEN DESCRIPTION

In accordance with an embodiment of the present invention, FIG. 1 shows a drilling system 100 in a wellbore 102. The drilling system 100 includes a drill string 104, a drill bit 106 and a MWD (measurement while drilling) tool 108. It will be appreciated that the drilling system 100 will include additional components, including drilling rigs, mud pumps and other surface-based facilities and downhole equipment.

The MWD tool 108 includes one or more sensors 110, an encoder module 112 and an acoustic pulse generating module, or pulser 114. It will be appreciated that the MWD tool 108 may include additional components, such as centralizers. The sensors 110 are configured to measure a condition on the drilling system 100 or in the wellbore 102 and produce a representative signal for the measurement. Such measurements may include, for example, temperature, pressure, vibration, torque, inclination, magnetic direction and position. The signals from the sensors 110 are encoded by the encoder module 112 into command signals delivered to the pulser 114.

Based on the command signals from the encoder module 112, the pulser 114 controllably adjusts the flow of fluid through the pulser 114. The rapid variation in the size of the flow path through the pulser 114 increases and decreases the pressure of drilling mud flowing through the MWD tool 108. The variation in pressure creates acoustic pulses that include the encoded signals from the sensors 110. The pressure pulses are transmitted through the wellbore 102 to a receiver 116 and processed by surface facilities to present the driller or operator with information about the drilling system 100 and wellbore 102.

The sensors 110, encoder module 112 and pulser 114 of the MWD tool 108 are operated using electricity. The electricity can be provided through an umbilical from the surface, from an onboard battery pack, through the operation of a generator or through some combination of batteries, generators and umbilicals.

Turning to FIG. 2, shown therein is a cross-sectional depiction of the pulser 114. The pulser 114 includes a housing 118, an annulus 120, a central bore 122, a piston assembly 124 and an orifice 126. The housing 118 isolates the internal components of the pulser 114 from the external wellbore 102. Drilling fluid moving through the pulser 114 passes through the annulus 120 and the orifice 126.

The piston assembly 124 includes a piston shaft 128, a piston 130 and a poppet valve 132. The piston 130 and poppet valve 132 are connected to, and configured for movement with, the piston shaft 128. The piston 130 is sized to fit in close proximity within the central bore 122. The piston assembly 124 is driven by a drive assembly 134 that produces the selective, rapid and bidirectional movement of the piston shaft 128, piston 130 and poppet valve 132 within the central bore 122. In some embodiments, the drive assembly 134 includes one or more solenoids that are configured to selectively reciprocate the piston shaft 128 in response to the application of electrical control signals.

When deployed, the piston shaft 128 extends and forces the poppet valve 132 into the orifice 126 to reduce flow through the pulser 114. When withdrawn, the piston shaft 128 retracts and removes the poppet valve 132 from the orifice 126 to increase flow through the pulser 114. The sequenced reduction and increase of flow through the pulser 114 creates pressure waves that carry encoded information from the sensors 110. It will be understood that the piston assembly 124 will reciprocate rapidly within the central bore 122 for extended periods of time during use.

Turning to FIG. 3, shown therein is a perspective view of the piston 130. The piston 130 includes a proximal end 136, a distal end 138 and a central portion 140. The central portion 140 includes a ring seat 142 within which a wear ring 144 is installed. The wear ring 144 provides a low friction interface between the piston 130 and the central bore 122 to facilitate reciprocation of the piston assembly 124 and prolong the useful life of the pulser 114. In some embodiments, the wear ring 144 is manufactured from a temperature and chemical resistant thermoplastic that resists wear and provides a desirable bearing surface. Suitable materials include ultra-high molecular weight polyethylene, oil-impregnated nylon and ceramics. The incorporation of the durable wear ring 144 presents a significant advantage over the high-friction seals used in prior art piston assemblies.

It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the scope and spirit of the present invention. 

What is claimed is:
 1. An acoustic pulse generating component for use in connection with a downhole drilling tool, the acoustic pulse generating module comprising: a piston assembly, wherein the piston assembly includes a piston having a wear ring; and a drive assembly configured to move the piston assembly.
 2. The acoustic pulse generating component of claim 1, wherein the wear ring comprises a thermoplastic wear ring.
 3. The acoustic pulse generating module of claim 2, wherein the wear ring comprises an ultra-high molecular weight polyethylene wear ring.
 4. The acoustic pulse generating module of claim 1, wherein the wear ring comprises an oil-impregnated nylon wear ring.
 5. The acoustic pulse generating module of claim 1, wherein the wear ring comprises a ceramic wear ring.
 6. The acoustic pulse generating module of claim 1, wherein the piston comprises: a proximal end; a distal end; a central portion between the proximal end and the distal end; and a ring seat within the central portion, wherein the wear ring is seated in the ring seat.
 7. The acoustic pulse generating module of claim 1, wherein the drive assembly comprises one or more solenoids configured to rapidly reciprocate the piston assembly within the pulse generating module.
 8. A drilling tool comprising: a sensor; an encoder operably connected to the sensor; and a pulser operably connected to the encoder, wherein the pulser comprises: a piston assembly, wherein the piston assembly includes a piston having a wear ring; and a drive assembly configured to move the piston assembly.
 9. The drilling tool of claim 8, wherein the wear ring comprises a thermoplastic wear ring.
 10. The drilling tool of claim 8, wherein the wear ring comprises an ultra-high molecular weight polyethylene wear ring.
 11. The drilling tool of claim 8, wherein the wear ring comprises an oil-impregnated nylon wear ring.
 12. The drilling tool of claim 8, wherein the wear ring comprises a ceramic wear ring.
 13. The drilling tool of claim 8, wherein the piston comprises: a proximal end; a distal end; a central portion between the proximal end and the distal end; and a ring seat within the central portion, wherein the wear ring is seated in the ring seat.
 14. The drilling tool of claim 8, wherein the drive assembly comprises one or more solenoids configured to rapidly reciprocate the piston assembly within the pulse generating module.
 15. The drilling tool of claim 8, wherein the piston assembly further comprises: a piston shaft; and a poppet valve.
 16. The drilling tool of claim 16, wherein the piston has an outer diameter and wherein the pulser further comprises: a central bore having an inner diameter, wherein the inner diameter of the central bore is nominally the same as the outer diameter of the piston; and an orifice, wherein the orifice is sized to admit the poppet valve.
 17. A measurement while drilling (MWD) tool comprising: at least one sensor configured to output a measurement signal representative of a measurement of a condition selected from the group consisting of torque, inclination, magnetic direction and position; an encoder configured to encode the measurement signal into a command signal; a pulser operably connected to the encoder and configured to transmit an acoustic signal through a fluid medium in response to the command signal, wherein the pulser comprises: a piston assembly, wherein the piston assembly includes a piston having a wear ring; and a drive assembly configured to move the piston assembly.
 18. The MWD tool of claim 17, wherein the wear ring is manufactured from a material that exhibits a low coefficient of friction.
 19. The MWD tool of claim 18, wherein the wear ring is manufactured from a material selected from the group consisting of plastics and ceramics.
 20. The MWD tool of claim 19, wherein the wear ring is manufactured from a material selected from the group consisting of ultra-high molecular weight polyethylene and oil-impregnated nylon. 